A round table has no corners, a square table has only four corners and a hexagonal table has six corners.

The four corners of the round table can be folded down with elastic hinges, and then the desktop becomes a square table.

1. Before making a round table, make a square table. The diagonal length of this square table is equal to the diameter length of the round table. After the square table is finished, make a chord length equal to the side length of the square table on the four sides. The arc length is equal to the diagonal of the square table divided by two, the quotient multiplied by π, and the product divided by four. According to this size, four identical square table accessories are made, and then their chords facing the sides of the square table are installed on the four sides of the square table with elastic hinges respectively. Lift this accessory and lay it flat with the square table. At this time, the square table became a round table. When the round table is not used, four accessories are folded down, and the round table becomes a square table. This is the change or operation process of the round table becoming a square table.

2. According to the above discussion and operation flow, the four accessories in four directions of the round table are folded down to form a square table.